1. Field of the Invention
This invention relates to overhead projectors, specifically to methods and accessories that are used with overhead projectors to color highlight and align projected transparency images as a means to capture and guide audience attention.
2. Description of the Background Art
Many presenters depend upon overhead projection as a primary communications media particularly in business, industry and education. Transparency costs are low and preparation is quick and easy. The pervasive method of transparency preparation is simply to xerographically copy the originals onto standard-size monochrome transparencies. The majority of presentations consist of a series of unmodified, unmounted, unbound single sheets. It is a nearly universal practice to project this series without the aid of any accessory to highlight or align image areas. Because of the convenience and economy, this presentation approach endures in spite of major shortcomings including: (1) loss of attention from ineffective means to highlight image areas and points of interest to pace audience focus; (2) low visual interest inherent in strictly black and white transparencies; and (3) distraction from transparency misalignment.
The prior art shows very few accessories to manipulate the highlighting of projected image areas. Rather, the majority of the prior art shows accessories to provide containment or registration for superimposed transparencies. The choice to superimpose transparencies to highlight images areas suffers a range of disadvantages including complicated transparency preparation and registration devices and typically noncompact arrangements that require transparencies to be punched with holes, slits, or notches. Registration, of necessity, restricts transparency positioning, which is not always desirable. Presenters must often adjust the transparency position to compensate for obstructed visibility. Much of the prior art shows auxiliary stages, platens, frames or holders which elevate the transparency above the plane of the projection stage. Depending upon the type of overhead projector, this elevation may result in projected images distorted by double imaging.
U.S. Pat. Nos. 3,642,359 and 3,640,613 to Kitch, 3,537,792 to Furniss et al., 3,544,211 to Albee, 3,438,702 to Milhaupt et al., 3,269,261 to Porter, and 3,709,590 to Bisberg show overhead projection devices having relatively bulky and complex auxiliary projection stages or frames which elevate the transparencies above the projection plane. No means are provided for highlighting other than registering superimposed transparencies. The buildup of superimposed transparencies, when used on projectors with reflective projection stages, causes distortion. Also, these devices require special preparation of the transparencies including either carrier mountings, holes, slits, or notches for fixed registration. Further, the methods shown for registration, mounting, or containment occlude the margin areas of the transparency.
U.S. Pat. No. 4,203,659 to Constantine et al. offers an improvement over the above noted patents. Although relatively bulky, the Constantine invention allows closer proximity of the transparency to the projector's stage.
Provided in U.S. Pat. Nos. 4,732,468 to Wright and 4,787,738 to Joffe are projection stage mechanisms providing registration for superimposed transparencies. The devices shown in these patents require that holes must be punched in the margins of the transparency, thereby fixing the location of the transparency relative to the register. No method of highlighting is provided for these devices.
Also, disclosed in U.S. Pat. Nos. 3,334,540 to Wright and 3,542,463 to Klein are overhead projection accessories which lack any specific highlighting mechanisms. Wright's device occludes margins and in the preferred embodiment uses an auxiliary stage which is not compact and which elevates the transparencies. While Klein's device permits transparencies to lie flat upon the projection stage, it requires projector modification for mounting and is neither compact nor portable.
Considering the foregoing devices, what is needed most among presenters is neither unhighlighted registration or containment of transparencies, but rather a method to control audience attention that is coupled with a simple means for repeatable alignment along one axis in cooperation with a means to highlight with color borders and selected areas and points of the projected image in synchronism with the presentation. The following patents present devices that attempt, among other goals, to incorporate an element for highlighting into the mechanisms.
U.S. Pat. Nos. 3,998,535 to Clarke and 4,632,529 to Levin show accessories which provide limited alternative highlighting mechanisms. Both Clarke and Levin however, show noncompact auxiliary platforms which cause double image distortion on projectors with reflective projection stages. In Clarke the color-tinted overlay strips used to highlight specific areas are supported by planar strips along the edges of the auxiliary stage. The overlay strips for highlighting are thus elevated causing possible double image distortion. The highlighting overlays can only be oriented in either of two mutually perpendicular directions and are constrained in their shape and length to span the width of the projection stage. In Levin, the auxiliary stage includes orthogonal stop surfaces for transparency abutment to register superimposed transparencies. Levin also shows a cursor device consisting of a flexible strip or sheet attached to the top of a guide block. Since the guide block slides along the guide surface of the auxiliary stage, this highlighting mechanism is restricted to motion and position in only one axis. The cursor strip does not lie flat upon the auxiliary stage. Thus, double image distortions result with the use of projectors having reflective projection stages. The Levin device further incorporates a fixed opaque border into the auxiliary stage which occludes the transparency margins.
U.S. Pat. No. 3,832,050 to Johannsen shows a pointing device for a projection apparatus comprised of a electromechanical mechanism to move two transparent strips such that they intersect at the desired point of interest in the projected image. This device is complex and, due to its mechanical integration into the projection apparatus, is not portable. Further, the device cannot highlight borders or outline areas of the projected image.